The present invention relates to an electro-optical system for detecting the presence of an object and more particularly to an electro-optical system for detecting the presence of an object within a predetermined detection region.
It is often desirable, particularly in the field of industrial control applications, to be able to determine electro-optically the presence of an object within a predetermined detection region. For example, one might want to detect the presence of an object as it passes by on a moving conveyor belt. As can be appreciated, one problem which may be associated with making such determinations is the indication of false positive signals generated by the presence of objects beyond the outboard edge of the conveyor belt and/or before the inboard edge of the conveyor belt.
In U.S. Pat. No. 4,899,041 to Fetzer et al., a light sensor for detecting an object in a certain distance range is described. The light sensor has a light transmitter which radiates the light along an axis of a transmitter system and two light receiving systems which pick up the light scattered back from an object to be detected along a receiving system axis. A light sensitive element has three detection zones arranged in a row of which the outer zones each receive light via one of the receiving systems from a sensing zone and of which the central detection zone accepts light via both light receiving systems from the background region of the field of view of the light sensor. An output signal which is used for object recognition is obtained by additive superposition of the signals of the detection zones associated with the scanning region and by difference formation with the signal from the detection zone associated with the background region. The sensing distance is adjusted by adjusting a roof edge mirror arranged in front of the light sensitive element.
In U.S. Pat. No. 4,655,586 to Stauffer, an adjustable zone proximity sensor is described. The sensor projects a beam of radiation towards the object. The return radiation is focused on a plane containing two detectors which are mounted substantially edge to edge. When the object is at the exact desired distance, the return radiation will be focused in the area between the two detectors so both of the detectors will receive the same amount of radiation. Thereafter, as the object moves away from the exact range, the image will move onto one of the detectors and away from the other, while if the object moves closer than the exact range, the image will move onto the other of the detectors and away from the first. With appropriate electronics it can be determined whether the return radiation is falling primarily on the one detector, the other detector, or is between them. This then determines whether the object is too far, too near, or at the right distance, respectively.
In U.S. Pat. No. 4,936,676 to Stauffer there is disclosed a surface position sensor utilizing a beam of energy reflected from the surface through an optical receiver to a detector wherein an energy blocking member having a receiver aperture permits only energy substantially parallel to the optic axis of the optical receiver to pass through to the detector.
Other patents of interest include U.S. Pat. No. 4,975,565 to Schmidt et al., U.S. Pat. No. 4,971,440 to Winckler et al., U.S. Pat. No. 4,815,840 to Benayad-Cherif et al., U.S. Pat. No. 4,775,235 to Hecker et al., U.S. Pat. No. 4,490,037 to Anagnostopoulos et al., U.S. Pat. No. 4,332,468 to Stutzle, U.S. Pat. No. 3,954,339 to Atwood et al., U.S. Pat. No. 3,942,894 to Maier, U.S. Pat. No. 3,918,814 to Weiser, U.S. Pat. No. 3,785,738 to Hoppke, U.S. Pat. No. 3,558,230 to Fowler, and U.S. Pat. No. 3,514,620 to Wiggerman.